Spiral wound membrane permeate carrier with thin border

Abstract

A permeate carrier to be described in detail below has side edges, alternatively called borders, that are thinner than a central part of the permeate carrier. Adhesive is applied to the side edges to form a seal when a membrane leaf is formed around the permeate carrier. After the membrane leaf is wound around a central tube, the side edges extend in a spiral around the central tube. The transition between the side edges and the central part of the permeate carrier helps prevent adhesive from flowing into the central part of the permeate carrier. The reduced thickness of the side edges also reduces an increase in diameter at the ends of an element that might otherwise be caused by the adhesive.

The invention claimed is: 
     
       1. A permeate carrier for a spiral wound membrane comprising:
 a woven sheet having: 
 a central portion having a front edge and a pair of side edges generally perpendicular to the front edge; and, 
 one or more borders along one or both side edges of the central portion, 
 wherein the central portion and the one or more borders having a series of raised ribs extending from a front surface of the permeate carrier, the raised ribs running generally parallel to the pair of side edges and defining permeate channels on the front surface, 
 wherein the raised ribs in the central portion extend further from the front side than the raised ribs in the one or more borders such that the one or more borders are thinner than the central portion, and 
 wherein a first spacing between the raised ribs in the central portion is substantially equal to a second spacing between the raised ribs in the one or more borders. 
 
     
     
       2. The permeate carrier of  claim 1  wherein the one or more borders are at least 2 mil thinner than the central portion. 
     
     
       3. The permeate carrier of  claim 2  wherein the one or more borders are between 2 and 5 mil thinner than the central portion. 
     
     
       4. The permeate carrier of  claim 1  wherein the borders are initially of the same thickness as the central portion but have been compressed to be thinner than the central portion. 
     
     
       5. The permeate carrier of  claim 1  wherein the borders are knitted with one or more of a) thinner yarn, b) more deformable yarn, and c) or fewer, including no, wales per inch, relative to the central portion. 
     
     
       6. The permeate carrier of  claim 1  wherein the one or more borders have a width between 1 inch and 1.75 inches. 
     
     
       7. A spiral wound membrane comprising:
 two membrane sheets; 
 a permeate carrier between the two membrane sheets, the permeate carrier comprising: 
 a woven sheet having:
 a central portion having a front edge, and a pair of side edges generally perpendicular to the front edge; 
 one or more borders along one or both side edges of the permeate carrier; 
 wherein the central portion and the one or more borders having a series of raised ribs extending from a front surface of the permeate carrier, the raised ribs running generally parallel to the pair of side edges and defining permeate channels on the front surface; 
 wherein the raised ribs in the central portion extend further from the front side than the raised ribs in the one or more borders such that the one or more borders are thinner than the central portion; 
 wherein a first spacing between the raised ribs in the central portion is substantially equal to a second spacing between the raised ribs in the one or more borders; 
 
 wherein the permeate carrier is glued to the two membrane sheets at one or more the borders along one or both side edges. 
 
     
     
       8. The spiral wound membrane of  claim 7  wherein the one or more borders are at least 2 mil thinner than the central portion. 
     
     
       9. The spiral wound membrane of  claim 8  wherein the one or more borders are between 2 and 5 mil thinner than the central portion. 
     
     
       10. The spiral wound membrane of  claim 7  wherein the borders are compressed to be thinner than the central portion during gluing the two membranes to the borders. 
     
     
       11. The spiral wound membrane of  claim 7  wherein the borders are knitted with one or more of a) thinner yarn, b) more deformable yarn, and c) or fewer, including no, wales per inch, relative to the central portion. 
     
     
       12. The spiral wound membrane of  claim 7  wherein the one or more borders have a width for an adequate width of between 1 inch and 1.75 inches.